Background: To our knowledge, no study has assessed the validity of family history data provided by probands with adult-onset dystonia. Objective: To measure the sensitivity and specificity of interviewing patients with primary adult-onset dystonia as a method for obtaining information on dystonia in first-degree relatives. Participants: Seventy probands with primary adult-onset dystonia were asked to identify first-degree relatives who had dystonia. Available relatives were then directly examined by a trained neurologist. The validity of the probands' reports was tested against the neurologists' diagnoses. Results: Among 300 first-degree relatives who were examined, 26 received a diagnosis of dystonia. Only 7 of the 26 were identified by the probands' reports. Among the 274 relatives free of dystonia, the probands reported 5 as having dystonia. The probands' reports therefore yielded a sensitivity of 27.0% and a specificity of 98.2%. Conclusions: Because the family history method yields low sensitivity and incurs a risk of misclassification, it is of limited use in family studies of adult-onset dystonia. The only valid means of ascertaining dystonia among relatives remains neurological examination of at-risk subjects.
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